The invention relates to instrumentation for measuring velocity and/or distances and, in particular, relates to instrumentation for measuring the velocity or distance, or both, of an inspection vehicle travelling inside a ferromagnetic pipeline.
It is known to use mechanical devices to measure distances or velocities. Such mechanical devices work by reason of contact between the vehicle and the static surface over which it is moving usually by means of a wheel. However, mechanical devices suffer for inaccuracies owing to slippage or skidding of the contacting surface or to bouncing off the surface.
The present invention seeks to provide a system for measuring velocities and distances wherein the measuring apparatus does not physically contact the surface over which it is travelling.